Key result
Papillary muscles change length to keep the tip-to-mitral annulus distance constant during the cardiac cycle.
Why the study?
Basic information about the three-dimensional geometry of the mitral apparatus is lacking, limiting the use of mitral valve homografts.
Papillary muscle length dynamically changes to maintain a constant distance from its tip to the mitral annulus, suggesting that preserving the entire papillary muscle length is important in mitral valve homograft or stentless xenograft operations.
Answers are grounded in this paper and cite their sources.
Dynamic papillary muscle preservation may matter in mitral homografts; animal data leaves open human translation and practice change.
OBJECTIVES: Mitral valve homografts, despite theoretical advantages, are not widely used, in part because of lack of basic information about the three-dimensional geometry of the mitral apparatus. METHODS: Radiopaque markers were used in the study of eight closed-chest dogs under four conditions: (1) baseline, (2) caval occlusion, (3) tachycardia (atrial pacing), and (4) nitroprusside infusion. Using a cylindrical coordinate system. defined with the origin at the midpoint between the anterior and posterior commissures, and the left ventricular long axis (z-axis), defined by the origin and the left ventricular apex, DTIP-MA (the z-coordinate [millimeters] of the papillary muscle tip), was measured at 10 time points throughout the entire cardiac cycle. DBASE-MA (the z-coordinate of the papillary muscle base) and LPM (the length of the papillary muscle [millimeters]) were also measured. RESULTS: DTIP-MA varied slightly with time (p < 0.001 by analysis of variance), but the magnitude of change was negligible (< 0.9 mm) (e.g., DTIP-MA of the anterior papillary muscle was 20.7 +/- 2.7/20.8 +/- 2.8 [end-diastolic/end-systolic, mean +/- 1 standard deviation]; DTIP-MA of the posterior papillary muscle was 25.8 +/- 4.8/25.5 +/- 4.5). DTIP-MA was minimally influenced by the above perturbations. DBASE-MA and LPM of each papillary muscle, however, changed throughout the cardiac cycle (p < 0.001 by analysis of variance) by about 4 mm, and both parameters were dependent on loading conditions. CONCLUSIONS: Papillary muscle length changed to keep the DTIP-MA distance constant such that the papillary muscle and left ventricular wall functioned together as a unit ("J-shaped complex"). These results provide a physiologic rationale for measuring DTIP-MA, define its potential surgical usefulness, and imply that using the entire length of the donor's papillary muscle (i.e., maintaining the entire J-shaped complex) is important in operations in which homograft or stentless xenograft mitral valves are used.
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Komeda et al. (1997) studied Mitral apparatus geometry (n=8). Hemodynamic perturbations (caval occlusion, tachycardia, nitroprusside infusion) vs. Baseline was evaluated on DTIP-MA (z-coordinate of the papillary muscle tip) (p=<0.001). Papillary muscle length changed throughout the cardiac cycle to keep the distance from the papillary muscle tip to the mitral annulus constant.
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